We report the crystal growth of well-faceted single crystals of methylammonium lead iodide, CH 3 NH 3 PbI 3 , and detailed single crystal neutron diffraction structural studies aimed at elucidating the orientation of the methylammonium (CH 3 NH 3 + ) cation in the tetragonal and cubic phases of the hybrid inorganic−organic perovskite. Room temperature experiments reveal a tetragonal structure where the protonated amine substituent (−NH 3 + ) of the cation is disordered in four positions, each preferentially located near the neighboring iodine of the [PbI 6 ] octahedra, while the methyl substituent (−CH 3 ) is disordered in eight positions located near the body position of the unit cell. High temperature experiments show a cubic structure where the cation aligns along the [011] (edge), the [111] (diagonal), and the [100] (face) directions of the unit cell. The resulting site occupancy ratio suggests the CH 3 NH 3 + cation resides primarily along the [011] direction, in agreement with reported DFT calculations. One important feature that was observed for both tetragonal and cubic structures measured at 295 and 350 K, respectively, is the middle point of the C−N bond being located off-center from the high symmetry sites in the crystal structure, induced by the formation of hydrogen bond-like interactions between the −NH 3 + substituent of the organic cation and the iodine atoms of [PbI 6 ] octahedra.

Metal-organic frameworks (MOFs) are promising high surface area coordination polymers with tunable pore structures and functionality;h owever,al acko fg ood sizea nd morphological control over the as-prepared MOFs has persisted as an issue in their application. Herein, we show how arobust protein template,tobacco mosaic virus (TMV), can be used to regulate the sizea nd shape of as-fabricated MOF materials.W ew ere able to obtain discrete rod-shaped TMV@MOF core-shell hybrids with good uniformity,a nd their diameters could be tuned by adjusting the synthetic conditions,w hichc an also significantly impact the stability of the core-shell composite.More interestingly,the virus particle underneath the MOF shell can be chemically modified using astandardbioconjugation reaction, showing mass transportation within the MOF shell.Metal-organic frameworks (MOFs) are af amily of microporous crystalline materials with high specific surface areas and extended porosities,w hich have attained al evel of preeminence because of their synthetic tunability.AMOF is constructed by coordinating rigid organic struts to ametal ion or cluster node to form ac rystalline material with ad efined pore structure,p ore size,a nd chemical composition. [1] The seemingly infinite combination of metal nodes and organic struts has enabled highly tunable design strategies for specific needs, [2] such as gas storage, [3] sensing, [4] catalysis, [5] energy, [6] and in biomedical applications. [7] An issue arising in many of these applications,h owever, has been the difficulty in controlling the crystallite morphology,w hich typically yields bulk MOF powders with relatively large crystal size,random shape,a nd poor monodispersity.T here is an articulated [8] interest in controlling the morphology of MOF crystallites because of the need for nanometer scale uniformity in biomedical and optoelectronics applications.T he synthetic strategies so far employed to regulate the size and morphology of MOF crystals have generally involved the addition of metal-binding reagents such as ligands,s urfactants,o rp olymers with chelating functional moieties. [9] Although these strategies afford regulation of size,t he as-obtained MOF particles are typically several hundred nanometers in size. More recently,M OF core-shell nanoparticles in the 100 nm range with good monodispersity have emerged, [10] though control over shape is not always high, resulting in irregular spheres or cubes.Virus nanoparticles offer alevel of control unavailable in synthetic systems as the surface chemistry can be altered by either chemical or genetic manipulation. [11] We selected the tobacco mosaic virus (TMV), at ubular viral particle that contains 2130 identical coat proteins self-assembled around as ingle strand of RNA. Because it is 300 nm long and only 18 nm wide,t he anisotropy of the virus has made it an attractive target for applications in photonics, [12] light harvesting solar arrays, [13] and MRI contrast agents. [14] TMV is also attractive because it can be isolated in gr...

Vitrimers hold great promise as adaptive materials capable of shape reconfigurability, welding, and self-healing due to dynamic covalent reactions occurring above the vitrimer transition temperature (T v ). Previous literature reports the T v as one value influenced mainly by chemistry; however, literature also reports significant inconsistencies when measuring or identifying T v trends. Herein, we present unique data interpretation methods to analyze stress−relaxation and elongational creep results allowing for excellent agreement between multiple T v measurement methodologies. We also demonstrate that experimental parameters (e.g., heating rate and applied axial force) and catalyst concentration are crucial in dictating the T v range. Varying the catalyst concentration or sample heating rate shifts the T v up to 115 and 43 °C, respectively. Additionally, we present a kinetic model confirming the temperature dependence of the transesterification rate-limiting step, exhibiting excellent agreement with experimental data. Fundamentally understanding the T v will inform future design of vitrimers toward applications ranging from recyclable actuators to structural adhesives.

Semiconducting polythiophenes display electroactive properties which make them excellent candidates for applications as electroactive materials. Ability to undergo doping and to switch between different oxidation states allow tuning the chemical and physical properties of polythiophenes. Furthermore, the ability to integrate polythiophenes into copolymers, hybrid composites with metals and inorganic materials make them useful in electronic and biomedical applications. The capability to vary the properties of the final material with low production cost and high processability into thin films makes polythiophenes desirable materials for many applications. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 3327–3346

Recently, thermoset vitrimer polymers have shown significant promise for structural applications because of their ability to be reshaped and remolded due to their covalent adaptive network (CAN). In these vitrimers, the transesterification reaction is responsible for the CAN, where the efficiency of the reaction is controlled either by organic or by organometallic catalysts. Understanding the mechanism of the transesterification reaction in the bulk phase using direct experimental techniques is extremely difficult due to the highly cross-linked complex structure of thermosetting vitrimers. Therefore, we use solution-phase experiments to investigate the catalytic efficiency and to guide density functional theory (DFT) simulations of the transesterification reaction mechanism with catalysts triazabicyclodecene (TBD), zinc acetate (Zn(OAc) 2 ), 1-methylimidazole (1-MI), and dibutyltin oxide (DBTO). The estimated catalytic efficiency from the detailed DFT reaction path calculations follows the order TBD ≳ DBTO ≳ Zn(OAc) 2 > 1-MI, which agrees with the experimental results. In addition to reaction path modeling, the mechanism and the relative rates of the transesterification reaction are analyzed with the assistance of Fukui indices as a measure of electrophilicity and nucleophilicity of atomic sites and with partial charges. It was found that the sum of the nucleophilicity index of the base and the electrophilicity index of the acid of the bifunctional catalysts correlates with the S N 2 transition state and tetrahedral intermediate energies, which are related to the barrier of the rate-limiting step. This correlation provides a hypothesis for computational prescreening of potentially better catalysts that have an index in a range of values. These results provide a basis for understanding an important part of the mechanism of transesterification in vitrimer systems and may assist with designing new catalysts.